As device nodes shrink, narrow and high aspect ratio pillars become mechanically fragile and are susceptible to bending with stress or force imbalance during deposition. For example, silicon oxide pillars with high aspect ratio may be susceptible to such bending. The stress or force imbalance around the slender pillars may be caused by capillary force with a flowable chemical vapor deposition (FCVD) meniscus profile, stiction force between FCVD deposition and the substrate (e.g., caused by intermolecular interactions between dangling bonds), and/or localized stress due to surface roughness.
FIG. 1 is a schematic cross-sectional view that illustrates a portion of a semiconductor device 100 in which line bending has occurred between two pillars within the semiconductor device 100. As shown in FIG. 1, the high aspect ratio device structures are formed on a surface of a substrate. During processing, device pillars 102 should remain in a vertical orientation and walls 106 should not cross the openings 104 and contact adjacent walls 106 of the pillars 102. The walls 106 of the pillars 102 are subjected to capillary forces which cause the walls 106 of adjacent pillars 102 to bend towards one another and contact each other. Line bending results from the contact between walls 106 of adjacent pillars 102, ultimately causing closure of the openings 104. Stiction, for example, occurs at least at interaction points 108 between adjacent pillars. Line bending in general, and line stiction in particular, is undesirable because, for example, it prevents access to the openings 104 during subsequent substrate processing steps, such as further deposition steps.
Capillary forces also cause bending of materials in these structures which can create the undesired stiction, which can damage the semiconductor substrate. The aforementioned drawbacks are especially apparent on substrates with high-aspect-ratio semiconductor pillars during deposition processes occurring on the substrate. Line bending results from bending of the side walls, which form the high-aspect-ratio trench or via, towards each other due to capillary pressure across the liquid-air interface over the liquid trapped in the trench or via. Such line bending also occurs due to high aspect ratio of the pillars and elastic constant of the pillar itself. Features with narrow line width and high-aspect-ratios are susceptible to the difference in surface tension created between liquid-air and liquid-wall interfaces due to capillary pressure, which is also sometimes referred to as capillary force.
During deposition, uneven distribution of a relatively viscous flowable film into the openings 104 between each of the pillars also leads to further line bending due to the lack of flowability of the deposited film in between each of the pillars. Uneven distribution of deposition may also give rise to initial surface roughness of the film deposited in between each of the pillars. Line bending may also occur by non-uniform reaction of the surface of the film deposited in between the pillars with native oxide. Semiconductor processing is facing a steeply rising challenge in preventing line bending as a result of rapid device scaling advancements.
As a result, there is a need in the art for FCVD processes which reduce or eliminate line bending and localized stress due to deposition roughness.